Dual Structure of a Vanadyl-Based Molecular Qubit Containing a Bis(β-diketonato) Ligand

We designed [VO(bdhb)] (1′) as a new electronic qubit containing an oxovanadium(IV) ion (S = 1/2) embraced by a single bis(β-diketonato) ligand [H2bdhb = 1,3-bis(3,5-dioxo-1-hexyl)benzene]. The synthesis afforded three different crystal phases, all of which unexpectedly contain dimers with formula [(VO)2(bdhb)2] (1). A trigonal form (1h) with a honeycomb structure and 46% of solvent-accessible voids quantitatively transforms over time into a monoclinic solvatomorph 1m and minor amounts of a triclinic solventless phase (1a). In a static magnetic field, 1h and 1m have detectably slow magnetic relaxation at low temperatures through quantum tunneling and Raman mechanisms. Angle-resolved electron paramagnetic resonance (EPR) spectra on single crystals revealed signatures of low-dimensional magnetic behavior, which is solvatomorph-dependent, being the closest interdimer V···V separations (6.7–7.5 Å) much shorter than intramolecular V···V distances (11.9–12.1 Å). According to 1H diffusion ordered spectroscopy (DOSY) and EPR experiments, the complex adopts the desired monomeric structure in organic solution and its geometry was inferred from density functional theory (DFT) calculations. Spin relaxation measurements in a frozen toluene-d8/CD2Cl2 matrix yielded Tm values reaching 13 μs at 10 K, and coherent spin manipulations were demonstrated by Rabi nutation experiments at 70 K. The neutral quasi-macrocyclic structure, featuring nuclear spin-free donors and additional possibilities for chemical functionalization, makes 1′ a new convenient spin-coherent building block in quantum technologies.

The given chemical formula and other crystal data include the solvent molecules in the channels, whose contribution to the scattering of X-rays was removed using the SQUEEZE routine.Displacement ellipsoids are drawn at the 60% probability level while H atoms are depicted as spheres of arbitrary radius.The color code is the same as in Figure S13.S2 and S3.S2 and S3.6), yielding  r = 2.26×10 11 s and a hydrodynamic radius of 0.36 nm.
Simulation analysis of the spectra estimated for  r a lower limit of 1.90×10 11 s and an upper limit of 2.66×10 11 s, which in turn correspond to a hydrodynamic radius of 0.34 and 0.38 nm, respectively.

Figure S5 .
Figure S5.Graphical representation of estimated and calculated MWs.The dashed red lines represent the upper and lower limits of estimated MWs using each ECC.ECC DSE and ECC MERGE are from Ref. 2 while ECC Crockett et al. is the external calibration curve reported in Ref. 3 .The black and blue lines represent the calculated MWs of monomeric [VO(bdhb)] (1') and dimeric 1, respectively.

Figure S8 .
Figure S8.FT-IR spectra of H 2 bdhb (red), the crude material (blue), and crystalline 1h (green) in the region 4000-2000 cm −1 (top) and 2000-400 cm −1 (bottom).The presence of H 2 O and EtOH molecules is reflected by the broad O-H stretching signal observed around 3450 cm 1 .The intense bands of the proligand between 1724 and 1602 cm 1 , which contain contributions from C=O and C=C stretching, are red shifted by approximately 100 cm 1 upon coordination.

Figure S11 .
Figure S11.Background-subtracted PXRD pattern of the crystalline solid obtained upon transformation of 1h (black), recorded at room temperature and with Cu-K radiation.The figure also shows the PXRD patterns of 1m, 1a, and 1h simulated from their X-ray structures at 100 K using Mercury 2021.1.0, 5with a full-width-athalf-maximum of 0.15° in 2.

Figure S12 .
Figure S12.The Rietveld observed (blue line), calculated (green line) and difference curve (cyan line) of the refined pattern of the crystalline solid obtained upon transformation of 1h.The black curve at the bottom represents the weighted difference between the observed and calculated diffraction patterns.The ticks indicate the calculated positions of the reflections for the monoclinic (1m) and triclinic (1a) phases, with the color code indicated in the legend.

Figure S13 .
Figure S13.ORTEP-3 6 plot of the divanadium(IV) complex in 1h.Displacement ellipsoids are drawn at the 60% probability level while H atoms are depicted as spheres of arbitrary radius.Color code: pink (V), red (O), black (C and H).

Figure S14 .
Figure S14.ORTEP-3 6 plot of the divanadium(IV) complex in 1m.Displacement ellipsoids are drawn at the 60% probability level while H atoms are depicted as spheres of arbitrary radius.The color code is the same as in Figure S13.

Figure S15 .
Figure S15.ORTEP-36 plot of the divanadium(IV) complex in 1a, omitting rotational disorder of CH 3 groups.Displacement ellipsoids are drawn at the 60% probability level while H atoms are depicted as spheres of arbitrary radius.The color code is the same as in FigureS13.

Figure S16 .
Figure S16.ORTEP-3 6 side view of divanadium(IV) complexes stacked into columns in 1h, with potential CHO hydrogen bonds depicted as dashed lines.Molecules are related by unitary translations along z.

Figure S17 .
Figure S17.ORTEP-3 6 top view of two stacked divanadium(IV) complexes in 1h.Displacement ellipsoids are drawn at the 60% probability level while H atoms are depicted as spheres of arbitrary radius.The color code for the top molecule is the same as in Figure S13.The bottom molecule is translated by 1 along z and is depicted in grey.

Figure S18 .FigureFigure S20 .Figure S21 .
Figure S18.(Left) ORTEP-3 6 plot of three divanadium(IV) complexes related by a 3 1 axis in 1h, as viewed along z and with potential CHO hydrogen bonds depicted as dashed lines.(Right) The 1D helical chain of intermolecular dipolar interactions between metal centers spiralizing along a 3 1 axis in 1h, as viewed approximately orthogonal to z and including only the donor O atoms.The dashed lines highlight the shortest VV distances in the crystal [7.1488(4) Å].Displacement ellipsoids are drawn at the 60% probability level while H atoms are depicted as spheres of arbitrary radius.The color code is the same as in Figure S13.

Figure
Figure S22.X-band CW-EPR spectrum of a single crystal of 1h, measured at 50 K with the magnetic field along the c axis.

Figure S23 .
Figure S23.Variable-frequency ac susceptibility of 1h (left) and 1m (right) as a function of applied dc field, measured at 1.9 K.The solid lines represent the best-fit curves obtained using a generalized Debye model and the parameters reported in TablesS2 and S3.

Figure S24 .
Figure S24.Variable-frequency ac susceptibility of 1h (left) and 1m (right) as a function of temperature, measured in dc fields of 7200 Oe and 7500 Oe, respectively.The solid lines are the best-fit curves obtained using a generalized Debye model and the parameters reported in TablesS2 and S3.

Table S1 .
Crystal data and refinement parameters for

Table S2 .
Best-fit parameters for frequency dependent ac susceptibility curves of 1h. a a For each best-fit parameter ( T  S , , ,  S ) the second column gives the associated uncertainty.

Table S3 .
Best-fit parameters for frequency dependent ac susceptibility curves of 1m. a For each best-fit parameter ( T  S , , ,  S ), the second column gives the associated uncertainty.

Table S4 .
T 1 and T m fitting parameters.

Table S6 .
Differences in enthalpy and Gibbs free energy between syn and anti conformers of 1', along with their partition functions, computed at T = 298.15K and p = 1.00 atm, in the gas phase and in different solvents, viz.pure toluene, pure CH 2 Cl 2 and a mixture of toluene and CH 2 Cl 2 (1:1 v/v).